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BB10003 Biochemistry > Carbohydrates > Flashcards

Carbohydrates Flashcards

1
Q

Carbohydrates are

A
  • Important structural components
  • important component of nucleic acids
  • contribute to protein structure
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2
Q

What is a peptidoglycan?

A
  • forming the cell wall
  • Prokaryotes
  • cross linking peptides, mesh network
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3
Q

What are proteoglycans?

A
  • Eukaryotes

- Form extracelluar matrix, which form bulk around cells to protect

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4
Q

Monosaccharides, disaccharides and polysaccharides.

A

Mono - Fruits, veg, honey, nuts
Dis - Sugars, milk
Poly - Rice, potatoes, corn, wheat

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5
Q

Sugar is made up of

A
  • glucose and fructose
  • once glucose transporters are saturated, the body cannot absorb any additional sugar in the form of glucose .
  • due to transport mechanisms to pass through intestinal wall
  • fructose diff mech
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6
Q

Simple sugars are

A
  • either aldoses or ketoses
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7
Q

Glucose and galactose are

A

Aldoses

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8
Q

Fructose is a

A

Ketose

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9
Q

Aldoses contain

A

Aldehyde group

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10
Q

Ketoses contain

A

Ketone group

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11
Q

D-Glyceraldehyde and L-glyceraldehyde

A

Enantiomers, form mirror images due to chiral centres

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12
Q

Optical Isomerism

A
  • What happens when we shine light through a polarising filter?
    Turn detector to left to get max light - l
    Turn to Right - d
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13
Q

Glucose formed by

A

Photosynthesis

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14
Q

Fisher Convention/Projection

A
  • Worked out Glyceraldehyde had two forms
  • D and L
  • D OH on right
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15
Q

If a molecule has N chiral centres

A

2 to the power of N isomers (bel Van hoff rule)

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16
Q

In Isomers of Aldo-tetroses we call mirror images

A

Erythrose and Threose (D and L)

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17
Q

Erythro refers to

A
  • functional groups on same side of molecule
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18
Q

Aldehyde react with alcohol to form

A
  • hemiacetal
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19
Q

Ketone with alcohol to form

A
  • Hemiketal
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20
Q

How glucose forms into a ring

A
  • 2 possible conformations depending on which way round you form the ring
  • Alpha or Beta anomer
    1) OH-5 reacts with C1 aldehyde
    2) Forms hemiacetal of carbon no 1 position
    3) ring structures are reversible
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21
Q

Glucose can form 2 diff rings known as

A 
6 membered is Pyranose
5 membered is Furanose
(alpha and beta anomer of each)
C1 position OH down in alpha up in beta
- changes stability of 3D structure of rings
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22
Q

Beta form are more/less stable?

A
  • more stable
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23
Q

Two anomers of glucose called…

A

-pyranose and furanose

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24
Q

2 other examples of hexoses that are metabolised

A
  • galactose and mannose

- these are epimers of glucose

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25
Q

An epimer is a

A

Chirally opposite centre

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26
Q

Stability of diff anomers in free solutions varies

A
  • in manose its alpha which is more stable than beta
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27
Q

Stability can be measured by seeing

A

optical rotation over time

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28
Q

Most stable form of these enantiomers

A
  • Chair, can flip to boat though
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29
Q

Fructose features

A
  • forms a 5 carbon ring, can only form a furanose ring due to carbonyl in position 2
  • Beta and Alpha anomer
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30
Q

ATP features

A
  • Structure, 5 membered sugar ring, 3 phosphate groups on end.
  • phosphate bonds are thermodynamically unstable
  • High energy phosphate bonds
  • kinetically stable though
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31
Q

Hydrolysis of ATP

A
  • yield energy
  • converted to ADP and Pi
  • 4 oxygen groups neg charge disruputed around phosphate ion, gives stability
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32
Q

Standard conditions hydrolysis of ATP

A
  • room temp and pressure
  • 1 mol conditions
  • 30KJ/Mol of ATP
  • Hydrolyse to pyrophosphate
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33
Q

ATP acting as currency

A

positioned in between high and low energy levels

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34
Q

Constantly making ATP done by intermediary metabolism

A
  • breaking down in small steps
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35
Q

Glycolysis

A

1) Glucose –> 2 pyruvate
2) must put in ADP
3) and NAD cofactors
4) Pyruvate has 2 fates, go on to further oxidation or can produce lactate

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36
Q

2 ways in which glucose enters body

A

Facilitated diffusion transporters - GLUT

Sodium linked active transporters - SGLT

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37
Q

GLUT 2 transporters allows

A

Both glucose and fructose into cells

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38
Q

Insulin use…

A
  • control expression on cell surface of GLUT 4 transporter
  • short term it will enable increase in transport
  • long term changes in glucose metabolising enzymes
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39
Q

Once glucose is inside the cell glycolysis happens…

A

1) Glucose acted on by hexokinase (PHOSPHOTRANSFER)
2) Base catalysed isomerization -Phosphohexose isomerase - glucose-6-phosphate switches to fructose-6-phosphate
3) Phosphofructokinase sticks another phosphate onto molecule. Fructose 6 - phosphate –> Fructose 1,6 - bisphosphate.
4) Adolase reaction, cleaves 1,6-bisphosphate into glyceraldehyde 3-phosphate and dihydroxyacetone phosphate (2 3C compounds formed)
5) Isomerisation by Triose Phosphate Isomerase. Dihydroxyacetone phosphate goes to Glyceraldehyde 3-Phosphate
6) Glyceraldehyde 3-Phosphate Dehydrogenase converts Glyceraldehyde 3-phosphate to 1,3-bisphosphoglycerate.
Transfer of proton.
7) Phosphoglycerate kinase then transfers 1,3-bisphospoglycerate to 3-Phosphoglycerate.
8) Phosphoglycerate mutase catalyses 3-Phosphoglycerate to 2-phosphoglycerate
9) Enolase reduces 2-phosphoglycerate to Phosphoenolpyruvate
10) Pyruvate Kinase - ATP reacts with phosphate group to form another molecule of ATP and form phosphoenolpyruvate (unstable intermediate) then isomerises into pyruvate

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40
Q

Hexokinase does

A
  • transfers phosphate group onto C6 on glucose via ATP (ATP consuming reaction)
  • requires magnesium
    (cofactor)
  • nucleophilic attack from glucose to phosphate
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41
Q

Aspartate residue does what in phosphotransfer?

A

destabilises OH group on C6 of glucose, allows OH to be more nucleophilic

42
Q

Hexokinase types and features

A

1,2,3 have high affinity, allosterically regulated bu G6P and ATP

  • Glucokinase Hexokinase IV has low affinity
  • example of induced fit model (excludes H2O from active clef)
43
Q

Evolution of Hexokinase lead to what structure

A
  • Mammalian HKs have a duplicated domain structure
  • one is regulatory domain, similar structurally
  • catalytic domain
  • AMP - relieve inhibitory affect of ADP when binding
44
Q

Liver Glucokinases

A
  • difference bwteen GK and HK 1-3 is that GK works at high glucose conc
  • low affinity
45
Q

Base catalysed isomerization

A
  • ring form broken
  • can happen by lysine taking a proton, get open chain which can be rearranged
  • enzyme which does this also has functions in signalling in immune system
46
Q

Chemical affect of Phosphate group

A
  • Make molecule charged (negative)

- phosphorus more electronegative

47
Q

Two biochemical effects of glucose phosphorylation

A

The –ve charge prevents facultative diffusion out of the cell
The electron-withdrawing effect increases reactivity of the saccharide

48
Q

Phosphofructokinase features

A
  • ATP (substrate) able to inhibit reaction
  • allosteric regulation of enzyme behaviour
  • rate of reaction becomes dependent on conc of regulatory molecules, ATP also a coregulator
49
Q

What does enzyme existing in tetromeric form allow?

A
  • Flip from active to inactive state
  • R state (active) stabilised by ADP binding at allosteric site
  • If a lot of ATP then ADP displaced from allosteric site so will then be T state (inactive) active sites closed off.
  • Citrate binds to allosteric site too to cause switch off
50
Q

Citrate function…

A
  • oxidative metabolism results in reduction of citrate
  • citrate then acts as an allosteric regulator to switch off phosphofructokinase and reduce production of pyruvate from glucose
51
Q

Phosphofructokinase exists in X isoforms?

A

Two

52
Q

Aldolase mechanism in bacteria

A
  • key amino acid which catalyses starts of with lone pair of electrons on lysine acting as a nucleophile to attack fructose 16 bisphosphate, form a Schiff base
  • then allows for a ketoenol reformation
  • assisted by acid residue.
  • aspartate
53
Q

Aldolase mechanism in Mammailian

A
  • aspartate replaced by tyrosine

- catalytic lysine as a nucleophile

54
Q

Aldolase general features

A
  • homo-tetramer
55
Q

Mechanism for Isomerisation stage 5

A

Endediol intermediate

- forms a transition state ^

56
Q

Glyceraldehyde 3-Phosphate Dehydrogenase function in stage 6

A

catalyses reduction of NAD and transphosphorylation of inorganic phosphates to the sugar backbone.

57
Q

NADH features

A
  • mediates redox transfer in cell

- structure of it allows it to switch between oxidised and reduced forms

58
Q

STAGE 6 Glyceraldehyde 3-Phosphate Dehydrogenase MECHANISM

A
  • enzyme forms intermediate via the nucleophilic donation of a bond from a cysteine group to the aldehyde end group on molecule.
  • then opens double bond and allows hydride ion to be transferred to NAD+ in reduction step.
  • then rearranges to release product
59
Q

STAGE 7 - Phosphoglycerate kinase then transfers 1,3-bisphospoglycerate to 3-Phosphoglycerate.

A
  • enzyme folds in on itself to stop water coming in
  • allows phosphate transfer in active clef without H2O
  • get 2 ATP back so far
60
Q

STAGE 8 - Phosphoglycerate mutase catalyses 3-Phosphoglycerate to 2-phosphoglycerate

A
  • transfer phosphate from 3-2 position
  • isomerase reaction
  • using Mg2+ cofactor
  • teteromeric enzyme
61
Q

WHAT CLASS OF REACTION IS - Enolase reduces 2-phosphoglycerate to Phosphoenolpyruvate

A
  • lyase reaction (hydro)
62
Q

Phosphoenolpyruvate is…

A

energetically unfavourable structure

63
Q

MECHANISM OF STAGE 9 Enolase reduces 2-phosphoglycerate to Phosphoenolpyruvate

A
  • Metal ion cofactor dependent system
  • taking electrons away from carbonyl group to anchor substrate
  • allowing base catalysed rearrangement
  • allows transfer of oxygen to a free proton to release water and enol
64
Q

Enolase is a what enzyme

A

Dimer

65
Q

Pyruvate Kinase is a what enzyme

A

Teteromeric

  • allosteric sites for (fructose1,6-bisphosphate and ATP)
  • They switch conformation state of enzyme from active to inactive
  • ATP drops compared to ADP enzyme becomes active and allows production of more ATP
66
Q

Pyruvate Kinase reaction points

A
  • irreversible reaction due to pull by enol-keto isomerisation
  • allosterically regulated by tetramer
  • inhibited by fructose1,6-bisphosphate and ato
67
Q

ATP YIELD AT END

A
  • 2 molecules of ATP from Phosphoglycerate kinase reaction and 2 from pyruvate kinase reaction
  • produce 4 but needed 2 to phosphorylate glucose-6-phosphate and fructose 1,6-bisphosphate
68
Q

Anaerobic conditions - lactate/ end point of glycolysis

A
  • pyruvate produces lactate
  • produce lactate also in microbiological reactions
  • microrganisms can produce ethanol
69
Q

Aerobic conditons - fate of pyruvate

A
  • metabolised to CO2 and H2O
70
Q

Fermentation products

A
  • use it for alcohol production
  • bread and yoghurt
  • Yoghurt produced by lactic fermentation
  • production of antibiotics
71
Q

How is NAD+ regenerated from NADH?

A
  • reduction of pyruvate to lactate regenerates NAD+
72
Q

Lactate dehydrogenase reaction

A

Pyruvate (ketone group) reduced to lactate (alcohol group)

73
Q

Lactate dehydrogenase two forms

A
  • muscle form - preference for pyruvate to lactate when low oxygen
  • heart form - preference for lactate to pyruvate in high oxygen
74
Q

In yeast

A
  • ADH

- pyruvate–>ethanal–>ethanol +CO2

75
Q

In humans is alcohol converted back to ethanal and NADH. There are 3 problems:

A

1) ethanal is toxic and damages proteins
2) excess NADH produced uses up NAD+
3) reduced gluconeogenesis from lactate in liver leading to hypoglycaemia

76
Q

Pyruvate is a…

A

an alpha keto-carboxylic acid

77
Q

Gluconeogenesis is…

A
  • amino acids –> pyruvate
  • fatty acids –> acetyl coA
  • Lactate –> pyruvate
  • all of which can be converted then back to glucose
78
Q

Gluconeogenesis is in the liver…

A
  • pyruvate enters mitochondria
  • pyruvate –> oxaloacetate –> malate –> malate out of mitochondria, oxaloacetate –> PEP –> Fructose16-bisphosphate –> Fructose 6-phosphate –> Glucose 6-Phosphate, Glucose
79
Q

3 irreversible steps in glycolysis

A

hexokinase G —-> G6P
phosphofructokinase F6P—-> FBP
pyruvate kinase PEP—-> pyruvate

80
Q

Essentially 3 irreversible steps in glycolysis- Hence 3 bypass steps are required for gluconeogenesis:

A

Glucose 6 phosphatase G6P —-> G
Fructose bis-phosphatase F(1,6)BP —-> F6P
PEP carboxykinase + OxA—-> PEP
Pyruvate carboxylase pyruvate —-> OxA

81
Q

Enzymes in Gluconeogenesis…

A
  • Pyruvate carboxylase converts pyruvate (3C ) to oxaloacete (4C)
  • Malate dehydrogenase converts oxaloacetate back to malate
  • Malate Dehydrogenase converts Malate to Oxaloacetate
  • PEP carboxykinase converts OAA to PEP
  • Fructose Bisphosphatase converts Fructose1,6-bisphosphate to Fructose6-Phosphate
  • Glucose 6-Phosphatase converts Glucose 6-to glucose
82
Q

Gluconeogenesis is opposite of

A

Glycolysis

83
Q

What does a check point do?

A
  • need check point at beginning of anabolic reaction so that we don’t make substrate when its not necessary
84
Q

Pyruvate Carboxylase does… IN MITOCHONDRIA

A

Pyruvate to Oxaloacetate by addition of CO2 and ATP, put carboxy group on 3rd C atom to make 4 Carbon

  • one molecule of ATP to drive that reaction
  • Glucose out of 2 pyruvates use 2 molecules of ATP for 2 OAA
85
Q

Pyruvate coarboxylase activity can have an x FUNCTION???

A

anaplerosis function (replenishing mitochondrial oxaloacetate)

86
Q

Pyruvate carboxylase is dependent on what?

A
  • Biotin as a cofactor and magnesium ions
  • it is a 4 domain enzyme
  • teteromeric structure
87
Q

Pyruvate Carboxylase is switched on by

A
  • acetyl CoA
88
Q

Pyruvate C domains

A
  • carboxyl transferase domain
  • allosteric linking domain
  • biotin carrier domain
  • biotin carboxylase domain
89
Q

Acetyl CoA function in Pyruvate C

A

2 step

  • CO2 forms complex with biotin
  • complex transfers carboxyl group to pyruvate to form OAA
90
Q

Transporter molecules in mitochondria membrane to allow

A

Mitochondria to transport Malate into cytosol (diffusion)

91
Q

Formation of Phospho enol Pyruvate

A
  • GTP coupled reaction

- OAA to PEP

92
Q

Regulators for Phosphofructokinase

A
  • Inhibitors ATP and citrate
  • High level of citrate cell is in a high energy state
  • AMP activator
  • F(2,6)BP - activator
93
Q

FBPhospatse regulators

A
  • AMP - Inhibitor
  • ATP, citrate - no effect
  • F(2,6)BP - inhibitor
94
Q

Glucagon and Insulin are major hormone regulators

A
  • Glucagon leads to raising blood glucose

- Insulin leads to lowering blood glucose

95
Q

Phosphofructokinase 2 - Insulin and Glucagon control this

A
  • its a bifunctional enzyme
  • has a kinase activity - activated by insulin
  • phosphatase activity 0 phosphorylated and inhibited by glucagon
  • regulate level of F26BP
  • Insulin stimulate glycolytic pathway
  • Glucagon will inhibit and stimulate gluconeogenic pathway
96
Q

Structure of Phosphofructokinase 2

A
  • Kinase and Phosphatase stuck together
97
Q

Insulin action - Short term

A

Increase in glucose transport via the GLUT4 transporter

  • Insulin receptor signalling stimulates GLUT4 exocytosis
  • GLUT4 translocates through multiple intracellular compartments
98
Q

Insulin Long Term effects

A
  • Decreased protein synthesis of gluconeogenic enzymes eg PEP-CK
  • Increased protein synthesis of glycolytic enzymes eg GK (glucokinase)
99
Q

Aldotetrose are unable to…

A

to form stable ring structures

100
Q

Phosphohexose isomerase mechanism involves an…

A

enediol intermediate

BB10003 Biochemistry (5 decks)

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